In recent years, development of lighting devices using an LED as a light source has been accelerated, considering that existing lighting devices consume much electric power and should be frequently replaced due to a short life span thereof.
Currently, lighting devices using an LED as a light source are replacing existing fluorescent lights or light bulbs. The lighting devices are installed on a ceiling of an interior of a building and illuminate a relatively wide area.
However, the lighting devices using surface light emission as lighting devices using LEDs according to the related art have different intensities of illumination at central portions and peripheral portions thereof.
This is because the light of LEDs disposed at the central portions can be emitted to the light dispersing plate on the front side, but the light of LEDs located at the peripheral portions cannot be directly input to the light dispersing plate as it is reflected by a frame on a lateral side of the LEDs.
Further, the surface light-emitting devices using LEDs according to the related art accommodate a substrate to which LEDs are mounted, and a window frame formed of a metal is used as a frame fixed to a ceiling. Then, since the window frame should be formed by separately manufacturing edge frames and be assembled, productivity is very low.
There are very many examples of surface light-emitting devices forming a window frame by assembling divided linear frames, and one of the examples is Korean Patent No. 10-0976274.
It is disclosed in Korean Patent No. 10-0976274 that a first main frame and a second main frame are coupled to each other using bolts to manufacture a main frame, that is, a window frame, and in surface light-emitting devices using LEDs according to the related art, and metallic linear frames are coupled to each other by bolts to manufacture a window frame providing a space for accommodating a substrate to which LEDs are mounted.
A gap is generated between the first main frame and the second main frame, and dust may be introduced through the gap or insects such as mayflies may enter the window frame.
The foreign substances such as dust and insects gather on an upper surface of a light dispersing plate, that is, on an inside of the lighting device, and accordingly, the brightness of the lighting device becomes gradually darker.
This problem can be solved by disassembling the lighting device and cleaning the light dispersing plate, but because the light dispersing plate is inserted into and fixed to a central portion of a window frame when being assembled in the main frame, that is, the window frame, it actually cannot be disassembled.
Accordingly, even when the life span of the LEDs is 10 years or more, the brightness of the lighting device is gradually reduced through introduction of foreign substances, making it difficult to use the lighting device for a long time.
As described above, because the main frame is assembled according to the related art, much time is spent in the assembly process and productivity is low. In particular, because the price of the lighting device is expensive due to use of a metal, an electric light rate reduction effect due to use of LEDs and a lamp exchange cost reduction effect are substantially low, making it difficult to commercialize the device.
In addition, because a metallic frame is used, weight is heavy, and when the LED surface light-emitting device installed on a ceiling falls due to a natural disaster such as an earthquake or a shoddy and faulty construction, it may be very dangerous. Further, because the main frame is fixed to a board installation frame of the ceiling using bolts and is fixed using a wire when being installed on the ceiling to prevent falling of the main frame, construction time is very long.